The present invention pertains to a wrapping apparatus, and in particular to a rotary stretch wrapping apparatus for quickly and efficiently providing a continuous wrap about a product.
The packaging of products to be shipped in a wrap of stretched plastic film is becoming increasingly popular. Stretch wrapping offers several advantages over the use of boxes, kraft paper, and other conventional packaging means. In particular stretch wrapping provides a durable, water resistant, and inexpensive covering for the product. Moreover, a product may be wrapped with great speed to thereby increase the resultant throughput.
One known stretch wrapping apparatus is disclosed in U.S. Pat. No. 4,317,322 to Lancaster et al., and entitled ROTATABLE FILM WRAPPING APPARATUS WITH WRAP CARRYING MECHANISM. Although such a machine will provide a continuous wrap of plastic film about a product, the machine is comprised of complex, inefficient, and unbalanced components. More specifically, the Lancaster patent '322 discloses a complex conveyor system for passing the product through the wrapping machine and an off-balance rotary structure adapted to circumscribe the product.
In a rotary stretch wrapping machine, the plastic film is tightly wrapped about the product and the conveyor upon which it rests. An ordinary conveyor is therefore useless since engagement of the film with the return path fights against the forward moving product. To overcome this problem, Lancaster has developed a complex conveyor system comprised of superimposed belts and an array of pulleys. However, fabrication of such a system involves high manufacturing and maintenance costs.
In a rotary stretch wrapping operation, the wrapping mechanism is spun about the product by a rotary support structure. In Lancaster '322, the rolls of film are mounted in a cantilevered manner to a circular rotary structure which is rotatably driven to effect wrapping of the product. These rolls, however, are frequently quite heavy and therefore engender large moment forces in the rotary structure as it is rotated about the product. These forces create a substantial imbalance in the structure which not only will hasten bearing wear, but also may pose a safety hazard.
In wrapping products with a rotary machine, problems may arise with respect to irregularities in the shape of the products to be wrapped. For instance, if a relatively flat product having a large width dimension is to be wrapped, a great deal more film will be needed to cover the width than will be needed to cover the height thereof. Yet, in many power driven machines, the film is dispensed at a constant rate irrespective of any irregularities. Hence, these machines, if operated on any but the most uniform products, will generate large amounts of slack in the film and thus foul the operation. An example of such an apparatus is disclosed in U.S. Pat. No. 4,418,510 to Lancaster, III et al., and entitled STRETCH WRAPPING APPARATUS AND PROCESS.
Additionally, wrapping machines are often used to either: (1) independently wrap products, wherein the film is sheared after each individual product is wrapped; or (2) wrapped in a somewhat sporadic manner wherein only one or a few products are wrapped in series at any one time. In these situations, the operator must manually feed the leading end of the film into a clamp or beneath the product with each product to be individually wrapped or with each leading product in a series of products to be wrapped. This feeding step is a slow and cumbersome task which requires a significant amount of down time for the apparatus.